Insulin molecule, illustration. Insulin is a protein hormone produced in the pancreas that regulates the metabolism of carbohydrates, proteins and fats. It does this by promoting the uptake of glucose from the blood into liver cells, skeletal muscle cells and fat cells. Disruption of insulin function can lead to diabetes. The primary structure of insulin was determined in the 1950s by Frederick Sanger and the three dimensional structure determined by Dorothy Hodgkin and colleagues in 1969.